FIG. 1 shows how data over cable service interface specifications (DOCSIS) traffic is currently transferred over a cable network 8. A server or other type of Internet Protocol (IP) network processing device 10, such as a personal computer (PC), is connected to a wide area network (WAN) 12. The device 10 communicates over cable network 8 with a device 22 or device 26. In one example, the device 22 is an Internet Protocol (IP) set top box (STB) and the device 26 is a PC. Of course the devices 10, 22 and 26 can be any type computing device configured for exchanging data over a network.
A communication link is established between a cable modem termination system (CMTS) 14 on the cable provider end of a hybrid fiber cable (HFC) plant 19 and a cable modem (CM) 20 on the customer premises end of the HFC 19. The CMTS 14 operates at a cable system headend and receives and sends IP traffic over the WAN 12 in one example using an Ethernet connection. Other types of network interfaces may also be used such as Dynamic Packet Transport/Resilient Packet Ring (DPT/RPR) or Packet-over-SONET/SDH (POS). Data is transferred from the CMTS 14 to the CM 20 over a downstream channel 16 and data is transferred from the CM 20 to the CMTS 14 over an upstream channel 18.
The cable network 8 is referred to as “narrowband” because a single radio frequency (RF) downstream channel 16 and a single RF upstream channel 18 are used over the HFC plant 19 for transferring data. The single downstream channel 16 supplies downstream IP connectivity to multiple cable modems 20 connected to the same cable plant 19. Each cable modem 20 demodulates and formats the downstream traffic for transport over IP network 21. Upstream IP traffic sent by the IP device 22 or 26 is modulated by the associated CM 20 onto the upstream channel 18 on the HFC plant 19. The CMTS 14 demodulates the signals on the upstream channel 18 and then sends the demodulated IP data to a device on WAN 12, such as device 10.
FIG. 2 shows the internal elements in one of the narrowband cable modems 20. A diplexor 30 connects to the two-way HFC plant 19. The diplexer 30 separates the frequency spectrum for downstream channel 16 from the frequency spectrum for upstream channel 18. A radio frequency (RF) tuner 32 selectively outputs different baseband frequencies 36 to a DOCSIS narrowband cable modem integrated circuit (IC) 37. The baseband frequencies 36 are converted into digital signals by an analog/digital (A/D) converter 38 and then fed into a quadrature amplitude modulation (QAM) demodulator 40.
Both a DOCSIS media access controller (MAC) 46 and a central processing unit (CPU) 48 process the data output from the QAM 40. The MAC 46 is an open system interconnection (OSI) layer-2 element that provides DOCSIS framing and signaling. The MAC 46 frames the data into IP packets or frames that are then sent to the appropriate device 22 or 26 over Ethernet interface 52. Other data may be received or sent by the cable modem 20 over a universal serial bus (USB) connection 41 via USB interface 42.
Data received over Ethernet interface 52 is formatted for transport over the upstream channel 18 of the HFC 19 by the MAC 46 and then otherwise processed by the CPU 48. The formatted data is modulated by a QAM modulator 51 and then converted into analog signals by a digital/analog (D/A) converter 50. The output of D/A converter 50 is then amplified by an amplifier 56 before being transmitted by the diplexor 30 over the upstream channel 18 of the HFC 19. For clarity, the physical connections between the different functional elements 38-52 have not been shown.
The bandwidth provided by a single downstream channel 16 and a single upstream channel 18 on the HFC 19 may not be sufficient for the bursty traffic that can be transmitted and received by a large numbers of cable modems 20. Therefore, current cable systems may not be capable of supporting applications that have a high average bandwidth such as constant bit rate (CBR) or variable bit rate (VBR) video.
Wideband cable systems have been developed that increase bandwidth in cable networks. Wideband packets are associated with logical wideband channels that extend over multiple RF cable channels. The multiple wideband channels contain a number of wideband transport sub-channels which can be dynamically adjusted for varying bandwidth requirements.
The narrowband cable modem architecture shown in FIGS. 1 and 2 does not support wideband cable systems. However, it would be desirable to leverage this conventional narrowband DOCSIS cable modem circuitry in new wideband DOCSIS systems. The present invention addresses this and other problems associated with the prior art.